Ultrastructural analysis of softwood fracture surfaces

• Published in: Wood science and technology 1994-07, Vol.28 (5), p.329-338
• Main Authors: Zink, A.G, Pellicane, P.J, Shuler, C.E
• Format: Article
• Language: English
• Subjects: Applied sciences; Exact sciences and technology; fracture; Pinus; Polymer industry, paints, wood; Properties and testing; Pseudotsuga menziesii; softwood; surfaces; ultrastructure; Wood; Wood. Paper. Non wovens
• ISSN: 0043-7719; 1432-5225
• DOI: 10.1007/BF00195280

The ultrastructural characteristics of fracture surfaces from southern pine and Douglas-fir specimens tested in tension at various angles to grain were examined. The fracture surface morphology was inspected using scanning electron microscopy. Three anatomical failure types were recognized: intercell failure, transwall failure, and intrawall failure. Certain failure characteristics were ascribed as a function of the magnitudes of parallel- and perpendicular-to-grain tension and parallel-to-grain shear present in the specimen. In specimens tested in parallel- and perpendicular-to-grain tension, the thick-walled latewood cells were found to fail in a combination of transwall and intrawall failure. The intrawall failures were usually at the S1-S2 interface. The more thin-walled earlywood cells were more likely to exhibit abrupt, transwall failures. At intermediate angles of load to grain, surfaces indicative of the type found in pure shear tests were predominant. Perpendicular- to-grain tension failures resulted in mostly intercell failures. Ray cells consistently exhibited transwall failures. The failure surface frequently changed planes in all loading modes. This path transfer was inevitably associated with material discontinuities in the wood. When the path did transfer, all three failure types were observed. No significant species effect was observed.